A comprehensive ground–flight testing approach for the dynamic performance of a critical space mechanism

On-ground testing of spacecraft is often a challenging task, including the design and development of dedicated setups, proper system modeling and data analysis techniques. However, sometimes ground-based testing may not be fully representative of the in-flight operation and a technology demonstration mission is flown to provide evidence of the maturity of critical technologies. This is the case of LISA Pathfinder (LPF), technology demonstration mission for LISA. We deal here with the LISA core instrument, namely the Gravitational Reference Sensor (GRS), which was successfully tested on board LPF. The focus is on the mechanism in charge of providing the initialization of its scientific phase, the grabbing, positioning and release mechanism (GPRM). The GPRM injects a reference mass hosted in the GRS into a pure geodesic trajectory, realizing essentially a second mission launch in reduced scale, characterized by very tight requirements. A dedicated strategy is put in place to provide a ground-based test of this function, starting from the concept up to involving an engineering qualifying model of the mechanism and developing a customized test approach, data analysis and result synthesis methods. The mechanism operation on board LISA Pathfinder however resulted anomalous, producing an out-of-nominal state of the reference mass. As a consequence, part of the extended mission phase was dedicated to perform some testing of the injection phase, to find risk-reduction strategies and understand the root cause of the anomaly. In this paper, we report on the result synthesis of the combined ground–flight testing campaign, proposing some mechanism development guidelines for LISA. • A launch-lock and release mechanism for a space mission is tested in-flight • The mechanism shows anomalous dynamics when a test mass is released into free-fall • The mechanism dynamics is interpreted through spacecraft telemetry data • A ground-based setup is developed to quantify the mechanism dynamic performance • Compatibility between flight and ground tests is verified, guiding mechanism design